This reverts commit 52b2afce2c.
The contact header is generated by the original sofia-sip library.
By adding the contact header explicit as user header it violates the
SIP RFC because sofia will add the Contact header to the BYE message as
well.
Let's fix the bugs in the freeswitch sofia-sip and make it compatible
(not bug compatible) with the original sofia-sip.
Change-Id: I712f17fecbc372d1e486e80673a548e281b37800